The present invention disclosed herein relates to an LED lamp using a nano-scale LED electrode assembly, and more particularly, to an LED lamp using a nano-scale LED electrode assembly in which a nano-scale LED device having a nano unit is connected to a nano-scale electrode without electrical short-circuit while maximizing light extraction efficiency.
The development of light emitting diodes (LEDs) has been actively promoted by succeeding in combination of a high-quality single-crystal gallium nitride (GaN) semiconductor by applying a low-temperature GaN compound buffer layer, by Nakamura et al., at Nichia Chemical Corporation in Japan, 1992. Such an LED is a semiconductor having a structure in which an n-type semiconductor crystal having a plurality of carriers, i.e., electrons and a p-type semiconductor crystal having a plurality of carrier, i.e., holes are junctioned to each other by using characteristics of a compound semiconductor, that is to say, a semiconductor device that converts an electrical signal into light having a wavelength band on a desired region to emit the light.
The LED semiconductor is called a revolution of light as a green material because the LED semiconductor has very low energy consumption due to high light conversion efficiency and is semi-permanent in the lifespan and environmentally friendly. Recently, as compound semiconductor technologies are developed, red, orange, green, blue, and white LEDs having high brightness have been developed. Also, the LEDs are being applied to various fields such as traffic lights, mobile phones, headlights for vehicles, outdoor electronic display boards, LED backlight units, and indoor/outdoor lightings, and also studies on the LEDs are being actively carried out. Particularly, a GaN-based compound semiconductor having a wide band gap may be a material that is used for manufacturing LED semiconductors which emit green and blue light and ultraviolet rays. Here, since a white LED device is manufactured by using a blue LED device, many studies with respect to the manufacture of the white LED device using the blue LED device are being carried out.
Also, due to the utilization of the LED semiconductor in various fields and studies on the LED semiconductor, an LED semiconductor having high output is required, and it is very important to improve efficiency of the LED semiconductor. However, it is difficult to manufacture the blue LED device having high efficiency. Drawbacks in improvement of efficiency of the blue LED device may cause the difficulty in manufacturing and a high refractive index between the manufactured LED and the GaN-based semiconductor. First, the difficulty in the manufacturing may be caused due to the difficulty in manufacturing of a substrate having the same lattice constant as the GaN-based semiconductor. A GaN epitaxial layer formed on the substrate may have many defects when the lattice constant with the substrate is significantly mismatched to deteriorate efficiency and reduce performance.
Next, light emitted from an active layer of the LED may not be escaped to the outside, but be totally reflected to the inside of the LED due to the high refractive index between the GaN-based semiconductor of the blue LED and the atmosphere. The totally reflected light may be reabsorbed to the inside to deteriorate the efficiency of the LED. The efficiency may be called light extraction efficiency of the LED device. To solve the above-described limitation, many studies are being carried out.
To utilize the LED device as lightings and displays, an LED device and an electrode for applying power to the LED device are required. Also, various studies on an arrangement of the LED device and two electrodes different from each other in connection with application purpose, reduction of a space occupied by the electrode, or a manufacturing method.
Studies relating to the arrangement of the LED device and the electrode may be classified into growth of the LED device and an arrangement of the electrode after the LED device is separately grown.
First, in studies on the growth of the LED device on the electrode, there is a bottom-up method in which the LED device and the electrode are formed and arranged at the same time through a series of manufacturing processes by using a method in which a lower electrode is formed on a substrate in the form of a thin film, and an n-type semiconductor layer, an active layer, a p-type semiconductor layer, and an upper electrode are successively stacked on the lower electrode and then etched, or the previously stacked are etched before the upper electrode is stacked and then the upper electrode is stacked.
Next, a method in an electrode is disposed after an LED device is separately and independently grown may be a method in which LED devices that are independently grown and manufactured through separate processes are disposed one by one on a patterned electrode.
The former method may have a limitation in that it is very difficult to crystallographically grow of high crystalline/high efficiency thin film and LED device, and the latter method may have a limitation in that light extraction efficiency is reduced to deteriorate light emitting efficiency.
Also, according to the latter method, although a three-dimensional LED device is connected to the electrode in a stand-up state in case of the general LED device, it is very difficult to stand up on the electrode in case of a nano-scale LED device having a nano unit. Korean Patent Application No. 2011-0040174 by the inventor of this application discloses a coupling link for easily coupling a nano-scale LED device having a nano unit to electrodes in a state where the LED device three-dimensionally stands up. However, it is very difficult to couple the nano-scale LED device to the electrode in the three-dimensionally stand-up state.
Furthermore, the LED devices that are independently manufactured have to be disposed one by one on the electrodes. However, in case of the nano-scale LED device, it is very difficult to respectively locate the LED devices on two nano-scale electrodes different from each other within a desired range. Also, even though the LED devices are disposed on the two nano-scale electrodes, defects such as electrical short-circuit between the electrode and the nano-scale LED may frequently occur, and it may be difficult to realize the desired electrode assembly.
Furthermore, the LED devices that are independently manufactured have to be disposed one by one on the electrodes. However, in case of the nano-scale LED device, it is very difficult to respectively locate the LED devices on two nano-scale electrodes different from each other within a desired range. Also, even though the LED devices are disposed on the two nano-scale electrodes, defects such as electrical short-circuit between the electrode and the nano-scale LED may frequently occur, and it may be difficult to realize the desired electrode assembly.
Furthermore, if the LED device three-dimensionally stands up on the electrode, and the electrode is formed on an upper portion of the LED device, photons generated in the active layer of the LED device may be totally reflected by a difference in refractive index between a surface of the standing-up nano-scale LED device and an air layer to deteriorate light extraction efficiency and also are blocked by the upper electrode and thus are not extracted to the outside. Thus, the photons may be absorbed into the active layer to significantly deteriorate the light extraction efficiency.
Korean Patent Registration No. 10-0523740 discloses a lamp using a light emitting diode. The lamp includes a first electrode part formed on a top surface of a substrate, p-type and n-type layers stacked and deposited on a top surface of the first electrode so as to be electrically connected to the first electrode part, and a second electrode part connecting the n-type layers to each other. In case of the lamp using the light emitting diode, the LED is manufactured by successively stacking the p-type and n-type layers on an upper portion of the electrode, but is not separately and independently manufactured. Thus, the LED may stand up on the electrode and be three-dimensionally coupled to the electrode.
Here, in case of the LED device that is separately and independently manufactured, i.e., the nano-scale LED device having a nano unit, there is a limitation in that it is impossible to stand up on the upper portion of the electrode so as to be three-dimensionally coupled to the electrode. Thus, the above-described method may be derived as one method for solving the limitation. However, the electrode may be disposed on each of upper and lower portions of the LED device through the above-described method. As a result, the limitation in which the photons generated in the LED device is totally reflected by the difference in refractive index and is not emitted to the outside due to the blocking of the electrode and thus captured in the electrode layer to deteriorate light extraction efficiency may not be solved.